A rare and quality George III Regency period cased mercury Fahrenheit thermometer by Thomas Rubergall of 27 Coventry Street, London.The thermometer is constructed from a single piece of engraved bone or ivory with the mercury tube affixed and housed in its original red leather case with velvet interior. It comes complete with catches and suspension ring.Thomas Rubergall was active from 1802 until 1854 in London and traded from three different addresses throughout those 52 years. Prices St, Soho from 1802 to 1805, 27 Coventry Street, London from 1805 to 1823 and then from there he seems to have moved to number 24 Coventry Street thereafter. Given the dates, we can therefore accurately date this pieces manufacture to within an 18 year period. Rubergall seems to have been from French descent and may be related to earlier well known Chelsea market gardeners of the eighteenth century with the same name. He was renowned enough to have been appointed optician to George III and mathematical instrument maker and optician to the Duke of Clarence (later William IV). An image of his trade card is provided.The site of the Rubergall’s shop was situated between Piccadilly and Leicester Square. A superb little scientific item from one of the most prominent scientific instrument retailers of the first half of the nineteenth century.